Overview of advanced water cooled reactors

In the second half of the 20th century nuclear power has evolved from the research and development environment to an industry that supplies 17% of the world’s electricity. In these 50 years of nuclear development a great deal has been achieved and many lessons have been learned. At the end of 1998, according to data reported in the Power Reactor Information System, PRIS, of the IAEA, there were 434 nuclear power plants in operation and 34 under construction. Over eight thousand five hundred reactor-years of operating experience had been accumulated.

Due to further industrialization, economic development and projected increases in the world’s population, global energy consumption will surely continue to increase into the 21st century. Based on IAEA’s review of nuclear power programmes [IAEA (1998)] and plans of Member States, several countries, especially in the Far East, are planning to expand their nuclear power capacity considerably in the next 15–20 years.

The contribution of nuclear energy to near and medium term energy needs depends on several key issues. The degree of global commitment to sustainable energy strategies and recognition of the role of nuclear energy in sustainable strategies will impact its future use.

Technological maturity, economic competitiveness and financing arrangements for new plants are key factors in decision making. Public perception of energy options and related environmental issues as well as public information and education will also play a key role in the introduction of evolutionary designs. Continued vigilance in nuclear power plant operation, and enhancement of safety culture and international co-operation are highly important in preserving the potential of nuclear power to contribute to future energy strategies.

To assure that nuclear power remains a viable option in meeting energy demands in the near and medium terms, new reactor designs, aimed at achieving certain improvements over existing designs are being developed in a number of countries. Common goals for these new designs are high availability, user-friendly features, competitive economics and compliance with internationally recognized safety objectives.

The early development of nuclear power was to a large extent conducted on a national basis. However, for advanced reactors, international co-operation is playing an important role, and the IAEA promotes international co-operation in advanced reactor development and application. Various organizations are involved, including governments, industries, utilities, universities, national laboratories, and research institutes.

Worldwide there is considerable experience in nuclear power technology and especially in light water reactor (LWR) and heavy water (HWR) technology. Of the operating plants, 346 are LWRs totaling 306 GW(e) and 31 are HWRs totaling 15 GW(e). The experience and lessons learned from these plants are being incorporated into new water cooled reactor designs. Utility requirements documents have been formulated to guide these activities by incorporating this experience with the aim of reducing costs and licensing uncertainties by establishing a technical foundation for the new designs.

The full spectrum of advanced water cooled reactor designs or concepts covers different types of designs — evolutionary ones, as well as innovative designs that require substantial development efforts. A natural dividing line between these two categories arises from the necessity of having to build and operate a prototype or demonstration plant to bring a concept with much innovation to commercial maturity, since such a plant represents the major part of the resources needed. Designs in both categories need engineering, and may also need research and development (R&D) and confirmatory testing prior to freezing the design of either the first plant of a given line in the evolutionary category, or of the prototype and/or demonstration plant for the second category. The amount of such R&D and confirmatory testing depends on the degree of both the innovation to be introduced and the related work already done, or the experience that can be built upon. This is particularly true for designs in the second category where it is entirely possible that all a concept needs is a demonstration plant, if development and confirmatory testing is essentially completed. At the other extreme, R&D, feasibility tests, confirmatory testing, and a prototype and/or demonstration plant are needed in addition to engineering. Different tasks have to be accomplished and their corresponding costs in qualitative terms are a function of the degree of departure from existing designs. In particular, a step increase in cost arises from the need to build a reactor as part of the development programme (see Figure 1.1).

Advanced design

Different types of new nuclear plants are being developed today that are generally called advanced reactors. In general, an advanced plant design is a design of current interest for which improvement over its predecessors and/or existing designs is expected. Advanced designs consist of evolutionary designs and designs requiring substantial development efforts. The latter can range from moderate modifications of existing designs to entirely new design concepts. They differ from evolutionary designs in that a prototype or a demonstration plant is required, or that insufficient work has been done to establish whether such a plant is required.

Evolutionary design

An evolutionary design is an advanced design that achieves improvements over existing designs through small to moderate modifications, with a strong emphasis on maintaining proven design features to minimise technological risks. The development of an evolutionary design requires at most engineering and confirmatory testing.

Innovative design

An innovative design is an advanced design which incorporates radical conceptual changes in design approaches or system configuration in comparison with existing practice. Substantial R&D, feasibility tests, and a prototype or demonstration plant are probably required.

Figure 1.1. Efforts and development costs for advanced designs versus departure from existing designs (Terms are excerpted from IAEA-TECDOC-936).

Large water cooled reactors with power outputs of 1300 MW(e) and above, which possess inherent safety characteristics (e.g. negative Doppler and moderator temperature coefficients, and negative moderator void coefficient) and incorporate proven, active engineered systems to accomplish safety functions are being developed. Other designs with power outputs from, for example, 220 MW(e) up to about 1300 MW(e) which also possess inherent safety characteristics and which place more emphasis on utilization of passive safety systems are also being developed. Passive safety systems are based on natural forces such as convection and gravity, making safety functions less dependent on active systems and components like pumps and diesel generators. Table 1.1 presents a list of advanced water cooled reactors under development¹.

TABLE 1.1. SURVEY OF ADVANCED WATER COOLED REACTOR DESIGNS UNDER DEVELOPMENT General Electric, USA in co-operation with Hitachi and Toshiba, Japan ABB Atom, Sweden

Westinghouse, USA, Genesi, Italy, EUR Nuclear Power International (NPI) General Electric, USA

Korea Electric Power Corp., Republic of Korea

National Nuclear Corp. (NNC), UK ABB Combustion Engineering, USA Siemens, Germany

Atomenergoprojekt/Gidropress, Russia Korea Advanced Institute of Science and Technology, Republic of Korea Atomic Energy of Canada, Ltd

Conceptual design

China National Nuclear Corp. (CNNC) China

Westinghouse, USA Hitachi Ltd., Japan Mitsubishi, Japan

Atomenergoprojekt/Gidropress, Russia Atomic Energy of Canada, Ltd.

Bhabha Atomic Research Centre, India

Conceptual design

Japan Atomic Energy Research Institute (JAERI), Japan

ABB Atom, Sweden

Japan Atomic Energy Research Institute (JAERI), Japan

1 The design status classification refers to the IAEA (1997a), Terms for Describing New, Advanced NPPs.

2 ESBWR (and JSBWR in Japan) is an enlarged version of GE’s SBWR design.

3 EP 1000 (in Europe) represents an enlarged version of AP-600.

4 Boiling light water cooled, heavy water moderated.

1For detailed descriptions of these designs see IAEA (1997c and 1997d).